The conversion of the square-wave transfer function into the corresponding sine-wave transfer function (i. e. MTF) via the Coltman's formula was performed by computer simulation. We expanded the Coltman's formula which is used for correction up to a maximum of twenty-five (25) terms, and then compared and discussed the difference of the results obtained using various numbers of correction terms. Our results showed that the use of first four (4) terms of the Coltman's formula was sufficient for correction, judging from the standard deviations of the resultant MTF values. A unique phenomenon, however, was noticed. Namely, if the first eight (8), eighteen (18), and twenty-three (23) correction terms were used, the MTF values might be reversed when the transfer function is still present at high spatial frequencies. If we set the MTF value at zero spatial frequency to unity (different from normalization), the results were the same as those corrected MTFs without reversion. However, when the correction terms up to five (5) or fourteen (14) were used, the reversion was present, even if the MTF value at zero spatial frequency was set to unity. Therefore a full consideration must be taken when using Coltman's formula, provided this phenomenon exists. Moreover, our calculated results showed that the MTF value at zero spatial frequency still could not be unity, even if the correction terms were up to 812. We concluded that the Coitrnan's correction expression is a function having considerably slow convergence.

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A method for generating repetitive flash x rays using a compact cold-cathode triode in conjunction with a two-stage Marx pulser is described. This flash x-ray generator consisted of the following components: a high-voltage power supply with a maximum voltage of 100kV, an energy storage condenser with a capacity of 100nF, a modified two-stage Marx pulser with a capacity during main discharge of 425pF, a turbo molecular pump, a trigger resistor of 3kΩ, and a flash x-ray tube. The two ceramic condensers were charged from 50 to 70kV, and the output voltages from the high-voltage pulser were about 1.8 times the charged voltages. The x-ray tube was of the triode type which was connected to the turbo molecular pump with a pressure of 6.7x10-4Pa and consisted of the following major devices: a rod-shaped long anode tip made of tungsten, a ring-shaped trigger electrode made of brass, a cylinder-shaped cathode electrode made of graphite, and a tube body made of acrylate resin. The durations of the flash x-ray pulses were about ips, and the x-ray intensity with a charged voltage of 70kV was about 320nC/kg at 0.5m per pulse. The repetitive frequency was less than 50Hz, and the maximum size of the focal spot was equivalent to the anode diameter of 3.0mm.

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The constructions and the fundamental studies for the repetitive pulsed x-ray generator utilizing a hot cathode diode are described. This generator consisted of the following components: a constant high-voltage power supply with a maximum voltage of 100kV, an energy storage condenser with a capacity of 100nF, a high-voltage pulser of a modified two-stage Marx type, and a hot-cathode diode. The two condensers in the high-voltage pulser were charged from 60 to 80kV, and the peak voltages (no-load) produced from this pulser were about 1.8 times the charged voltages. The condenser capacity during discharge was 425pF, and the effective durations of the pulsed x rays were about 10μs. The repetitive frequency was less than 50Hz, and the time-integrated x-ray intensity was about 60nC/kg at 0.5m per pulse with a charged voltage of 80kV. The tube current was considered to be a value of less than 0.5A, and the effective focal spot size was about 3.5mm.

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The first trial experiment for generating repetitive sub-millisecond pulsed x rays using a hotcathode triode in conjunction with a new type of grid control device is described. This generator consisted of the following essential components: a constant high-voltage power supply with a maximum voltage of 100kV, an energy storage condenser of 100nF, a repetitive grid control device, and a hot-cathode triode. In this first experiment, the energy storage condenser was charged from 40 to 60kV by a power supply, and the electric charges in the condenser were discharged repetitively by the grid electrode driven by the grid control device. The maximum grid voltage, the peak tube voltage, and the peak tube current were -08kV,60kV, and about 0.3A, respectively. The duration of pulsed x rays was primarily determined by the time constant of the grid control device and the cutoff voltage of thermoelectrons. The effective duration and the x-ray intensity were about 0.2ms and about 200nC/kg at 0.5m per pulse, respectively, with an initial grid voltage of -0.8kV and a condenser charged voltage of 60kV. The maximum repetitive frequency was about I kHz, and the effective focal spot size was less than 4mm.

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